Broach



March 17, 1942. H, H, G01-BERG l2,276,385

BROACH` Filed Deo. '7, 1940 ATTO Ys.

Patented Mar. 17, 1942 UNTED STATES T OFFICE BROACH Harry H. Gotberg,Detroit, Mich., assigner to Colonial Breach Company, Detroit, Mich., acorporation of Delaware 3 Claims.

The present invention relates te a breach for finishing hardenedinternal involute toothed forms and the like, such as internal involutegears er splines. It is also applicable to finish breaching of anyinternal toothed ferm in which the sides ef the teeth have a concavecurvature, whether involute, modified involute, or otherwise.

It is the practice in forming internal involute splines or gears tobreach the spline or gear to approximate final form prior to thehardening operation. Thereafter, the spline or gear is hardened and duete distortion which results from the hardening operation, it isnecessary to perform a finish breaching operation to bring the spline orgear to the desired final form. In this nishing operation, in theordinary case, very little material is removed but serious diicultiesare encountered because of the hardness of the material being cut. It isthe usual practice in such nish breaching te ferm a breaching tool, eachtooth of which is formed in the shape of the gear er spline tooth spaceand cuts the entire side profile of the gear er spline teeth en oppositesides of that space. In accordance with this practice, each breach toothhas an involute side cutting edge which must be relieved er backed eliand it is an extremely diicult and expensive hand operation t0 back ofian involute ferm cutting edge te a sharp edge without destroying theinvolute form. In addition, breaches of this type are subject teexceedingly heavy loads because of the width of the cut and the factthat the chip being curved transversely te the direction of the cutresists the necessary curling which must accompany its removal from thepart.

It has been suggested that the above mentioned diiiiculties may beovercome by providing a nishing breach in which the rst cutting tooth is'only slightly higher than the reet diameter of the internal gear orspline te be cut, but is of the full width of the final tooth form andby providing similar successive breach teeth of increasing radialprojection. These teeth cut only at their corners and remove the metalalong the involute tooth sides of the gear er spline progressively fromthe'roet to the crest of the gear or spline tooth space. This type ofbreach, however, performs all of its cutting en a sharp cerner with theresult that the corners of the teeth are subject te excessive'wear andare quickly broken down.

It is the object of the present invention to provide a nevel ferm ofnish breach adapted te finish internal involute splines er gears and thelike, in which the above mentioned dilliculties are overcome.

More specifically, it is the object of the present invention to providea iinish breach for internal involute gears or splinesvwhich is easy tomanufacture and to sharpen, which is not subject to excessive wear andwhich is easy to pull through the work.

Other objects and advantages of the invention will become apparent fromthe following specilication, the accompanying drawing, and the appendedclaims.

In the drawing:

Figure 1 is a trailing end View of a breaching tool in accordance withthe present invention;

Fig. 2 is a section of the breaching tool taken en the line 2--2 of Fig.1, parts being broken away;

Fig. 3 is an enlarged perspective View of one of the teeth of the breachintermediate its ends, and

Fig. 4 is an 'exaggerated diagrammatic illustration of the inannerinwhich successive teeth of the breach cut the werk piece. It illustratesa fragmentary tooth prele as viewed in a section transverse to the axisof the breach.

Referring to the drawing, particularly te Fig. 1, it will be seen thatthe breach illustrated as one embodiment of the present invention isadapted to finish an internal involute toothed form in a spline er gearor the like, the breach indicated at I0 being provided with a pluralityof rows 0f axially alignedteeth I I, each row being designed to finishthe space between adjacent teeth of the workpiece. The particular breachillustrated is adapted te form a straight spline or an internal spurgear, but it will be apparent that the invention is equally applicableto breaches designed V te finish helical internal splines or gears.

In the manufacture ef the breach I0, all of the teeth in each row areinitially formed with sides conforming to the prole of the desiredfinished ferm of the teeth of the workpiece. This form is illustrateddiagrammatically in Fig. 4 by the involute line I2 extending from thereet to the crest of the teeth. It may be notedr at this point that thecross-hatched area in Fig. 4 represents diagrammatically the materialwhich must be removed from the teeth space of the internal gear orspline in order tebring the internal gear or spline to its linishedferm. The side tooth profile of the unfinished internal gear or splineis therefore indicated diagrammatically by the line I3.

After the sides of all ef the breach teeth are given the desired form oifinal prei-ile indicated by the line I2, the first cutting tooth in eachrow is ground back to a ilat surface extending parallel to the axis ofthe broach indicated diagrammatically by the line I4 in Fig. 4. Theradial extremities of the fiat surface I4 terminate at the root andcrest of the sides I3 of the unfinished tooth profile. Each succeedingcutting tooth in each row is provided with a similar flat surface butthese flat surfaces on opposite sides of the succeeding broach teeth arespaced progressively further apart. Thus, on a tooth subsequent to thefirst tooth, the flat surfaces at the sides thereof may conform to theline I5 in Fig. 4, and a still later cutting tooth will have its fiatsurface conforming to the line I6 in Fig 4. It will be understood thatin the diagram Fig. 4, the thickness of the material to be removed isgreatly exaggerated for purposes -of clarity and that the flat surfaceson almost al1 of the cutting teeth will terminate like the flat surfacesindicated by the lines I5 and I6 at their radial extremities at pointsof intersection with the final desired tooth profile I2. As a result,the majority of the cutting teeth will be of a form like thatillustrated in Fig. 3 in which the sides of each tooth are provided withan intermediate flat portion I8 terminating at its radial extremities inouter and inner involute portions I9 and 2D which conform to the finalside profile I2 of the internal gear or spline tooth. The onlydifference between the tooth illustrated in Fig. 3 and the followingcutting teeth on the broach is that the flat surface I8 on thesucceeding teeth will be progressively reduced in radial extent asindicated best in Fig. 2, until Vadjacent; the trailing extremity of thebroach,

the flat surface I8 is of extremely narrow width.

Thereafter, the broach is provided with a plurality of finishing teethin the section indicated at 2l in Fig. 2, each of which retains the fullside profile I2 of the finished tooth. It will be understood that thelines I4, I5, and I5 in Fig. 4 do not represent the side profiles onsucceeding teeth but that the broach will be provided with a number ofteeth having profiles intermediate these two lines and that followingthe tooth having the fiat profile indicated I5 will be a num- 1 ber ofteeth having progressively smaller flat profiles approaching the finalinvolute form I2.

After the broach teeth are provided with the fiat side surfacesextending parallel to the axis of. the broach in the manner previouslydescribed, the front edges of these flat surfaces are relieved bygrinding back the flat, surfaces I8 at an angle to the axis of thebroach behind the front edges of those flat surfaces. No relief isprovided upon the residual involute side portions of the broach teethsuch as those indicated at I9 and 20 in Fig. 3. As a result, all of thecutting edges of the broach are lstraight cutting edges, such as thecutting edges 22 of the tooth illustrated in Fig. 3. These cutting edgesbeing straight edges are easy to back off or relieve and there is nodanger of impairing the final tooth form during the operation ofrelieving these straight edges because the edges do not conform to thefinal tooth form in any event. The involute toothed sections I9 and 2U,since they are not relieved, will remain accurate in size and form andtheir front edges perform no cutting operation.

The action of the broach in finishing an inr ternal gear or spline maybest be seen by reference to Fig. 4. In that figure, the crosshatchedportions indicated 24 are removed by the cutting teeth between the firstcutting tooth having the fiat profile indicated by the line I4 and thecutting tooth having the profile indicated by the line I5. Thecross-hatched portions indicated b-y the numeral 25 are removed by theteeth between the tooth having the straight prole indicated by the lineI5 and the tooth having the straight profile indicated by the line I6.Likewise, the cross-hatched material indicated by the line 26 is removedby the teeth between the tooth having the straight profile indicated bythe line I6 and the first finishing tooth in the section 2l, all ofwhich finishing teeth have the final involute tooth profile I2.

It will be noted in the case of the tooth having the profile indicatedI5 in Fig. 4 that it performs its cutting only at limited end portionsof the straight cutting edge indicated at 2'Iand that it does not cutintermediate 4the portions 21 or at the unrelieved involute edges spacedoutwardly of the cutting portions 21. In order to Ishow the nature ofthe cutting action, it was necessary to exaggerate in Fig. 4 the amountof metal to be removed, with the result that it would appear thatrelatively few teeth would cut in the manner of the tooth having thecutting edge I5. As a matter of fact, in the normal case, a majority ofthe cutting teeth would perform a cutting action only at their ends andwould cut progressively inwardly from opposite extremities of the toothside towards the center. The depth of cut of each tooth is relativelysmall being in the normal case in the order of .001 of an inch more orless on each `side of the tooth, with the result that the fact that norelieved cutting edges conform to the final involute shape does notinterfere with the cutting action.

In the diagram Fig. 4 is illustrated the cutting action when the broachis also designed to cut the tops and roots of the part. In this case,the tops and root areas are cut away by arcuate cutting edges havingtheir centers at the axis of the tool. The broach tooth having the sideprofile I4 is provided in that case with a root profile I4' and a crestprofile I4. Similarly, the tooth having the side profile I5 is providedwith a root prole I5 and a crest profile I5" and the tooth having theside profile I6 is provided with a root portion having a profile I6 anda crest profile I6". The final cutting teeth have root profiles I2 andcrest profiles I2.

Referring to the tooth shown in Fig. 3, the root cutting edge isindicated by the numeral 22' and the crest cutting edge by the numeral22". These root and crest portions are relieved in the usual manner, butsince the cutting edges are arcuate about the axis of the broach, nodifliculty is encountered in relieving them by an ordinary grindingoperation as in the case of involute cutting edges.

While the broach illustrated is adapted to cut at both the roots andcrests of the broach teeth, in the usual pline or internal gearfinishing operation no finishing is performed at the roots of the broachteeth, i. e. on the crests of the internal spline or gear, and in somecases no finishing is What is claimed is:

1. A broach for finishing internal involute tooth forms and the like,said broach having a row of cutting teeth for each tooth space of saidform, each cutting tooth of said row having a pair of convergingstraight relieved cutting edges for cutting on the sides of the tooth ofsaid form on opposite sides of said gear tooth space, respectively, eachstraight edge on the rst cutting tooth in said row being adapted to cutaway metal at only the inner and outer extremities of the side of theadjacent tooth of said form, the straight sides of each succeeding toothin said row being spaced further apart and effective to cut onprogressively approaching points on the adjacent tooth side of saidform, the later cutting teeth having the straight cutting edges thereofmerging at the extremities of said edges in unrelieved portionsconforming to the desired iinal side prole of the adjacent tooth of saidform.

2. A broach for finishing an internal involute toothed form and thelike, said broach having a row of cutting teeth for each tooth space ofsaid form, each cutting tooth in said row having a pair of straightrelieved cutting edges, one for cutting at the side of each tooth ofsaid form adjacent said space, the straight cutting edges on succeedingcutting teeth in said row being spaced progressively further apart andterminating at their ends at the points of intersection of said straightcutting edges with the desired nal profile of the sides of said teeth ofsaid form, the remainder of the sides of each broach tooth having anunrelieved edge conforming to the desired iinal prole of the sides ofthe teeth o said form.

3. A broach for finishing an internal involute toothed form and thelike, said broach having a row of cutting teeth for each tooth space ofsaid form adapted to cut the sides of the teeth on each side of saidspace, each cutting tooth having a pair of straight relieved cuttingedges, one for cutting the side of each adjacent tooth of said form,each straight cutting edge on the rst cutting tooth in said row beingadapted to cut at one extremity of the adjacent tooth side profile ofsaid form, the straight cutting edges on succeeding teeth in said rowbeing spaced progressively further apart whereby each succeeding toothcuts progressively along the side of the adjacent tooth of said formfrom said extremity,

each straight cutting edge on said succeeding cutting teeth thatintersects the desired iinal tooth profile of said form merging at thatpoint with an unrelieved edge having the desired nal profile of theadjacent tooth side of said form. HARRY H. GOTBERG.

